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Benzene is an
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or ...
chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be ...
with the
molecular formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes ...
C6H6. The benzene
molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion I ...

molecule
is composed of six
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
atoms joined in a planar ring with one
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a
hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structures, it is difficult to generalize furth ...
. Benzene is a natural constituent of
crude oil Petroleum, also known as crude oil and oil, is a naturally occurring, yellowish-black liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isoc ...

crude oil
and is one of the elementary
petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum Petroleum (), also known as crude oil and oil, is a #Latent heat of vaporization, naturally occurring, yellowish-black liquid found in geolo ...
s. Due to the cyclic continuous
pi bond In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s between the carbon atoms, benzene is classed as an
aromatic hydrocarbon Aromatic compounds are those chemical compounds (most commonly organic compound, organic) that contain one or more ring (chemistry), rings with pi electrons delocalized all the way around them. In contrast to compounds that exhibit aromaticity, al ...
. It is sometimes abbreviated
Ph
Ph
H. Benzene is a colorless and highly
flammable , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , demonym = Germans, German , g ...
liquid with a sweet smell, and is partially responsible for the aroma around petrol (gasoline) stations. It is used primarily as a
precursor Precursor or Precursors may refer to: *Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of unre ...
to the manufacture of chemicals with more complex structure, such as
ethylbenzene Ethylbenzene is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, cat ...
and
cumene Cumene (isopropylbenzene) is an organic compound that is based on an aromatic hydrocarbon with an aliphatic substitution. It is a constituent of crude oil and refined fuels. It is a flammable colorless liquid that has a boiling point of 152&nbs ...

cumene
, of which billions of kilograms are produced annually. Although a major
industrial chemical The chemical industry comprises the companies A company, abbreviated as co., is a Legal personality, legal entity representing an association of people, whether Natural person, natural, Legal personality, legal or a mixture of both, with a spe ...
, benzene finds limited use in consumer items because of its toxicity.


History


Discovery

The word "benzene" derives from "gum benzoin" (
benzoin resin Benzoin or benjamin (corrupted pronunciation) is a balsam Balsam is the resinous exudate (or sap) which forms on certain kinds of trees and shrubs. Balsam (from Latin balsamum "gum of the balsam tree", ultimately from Semitic, Aramaic ''busma' ...
), an aromatic resin known to European pharmacists and perfumers since the 16th century as a product of southeast Asia. An acidic material was derived from benzoin by sublimation, and named "flowers of benzoin", or benzoic acid. The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene.
Michael Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist A scientist is a person who conducts scientific research The scientific method is an Empirical evidence, empirical method of acquiring knowledge ...

Michael Faraday
first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name ''bicarburet of hydrogen''. In 1833,
Eilhard Mitscherlich Eilhard Mitscherlich (; 7 January 179428 August 1863) was a German chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist A scientist is a person who conducts Scientific m ...

Eilhard Mitscherlich
produced it by
distilling Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation. Dry distillation is the heating of solid materials to produ ...

distilling
benzoic acid Benzoic acid is a white (or colorless) solid with the formula C6H5CO2H. It is the simplest aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic ( ...

benzoic acid
(from
gum benzoin Benzoin or benjamin (corrupted pronunciation) is a balsamic resin obtained from the bark of several species of trees in the genus ''Styrax''. It is used in perfumes, some kinds of incense, as a flavoring, and medicine (see tincture of benzoin). I ...
) and
lime Lime refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany * Austra ...

lime
. He gave the compound the name ''benzin''. In 1836, the French chemist
Auguste Laurent Auguste Laurent (14 November 1807 – 15 April 1853) was a French chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist A scientist is a person who conducts Scientific me ...
named the substance "phène"; this word has become the root of the English word "
phenol Phenol (also called carbolic acid) is an aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), plane (geometry), p ...

phenol
", which is
hydroxylated In chemistry, hydroxylation is can refer to: *(i) most commonly, hydroxylation describes a chemistry, chemical process that introduces a hydroxyl group (-OH) into an organic compound. *(ii) the ''degree of hydroxylation'' refers to the number of O ...
benzene, and "
phenyl In organic chemistry Organic chemistry is a branch of that studies the structure, properties and reactions of s, which contain in .Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . Stu ...

phenyl
", the radical formed by abstraction of a hydrogen atom (
free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Ailments of unknown cause Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabo ...
H•) from benzene. In 1845,
Charles Mansfield
Charles Mansfield
, working under
August Wilhelm von Hofmann August Wilhelm von Hofmann (8 April 18185 May 1892) was a German chemist who made considerable contributions to organic chemistry. His research on aniline helped lay the basis of the aniline-dye industry, and his research on coal tar laid the gr ...

August Wilhelm von Hofmann
, isolated benzene from
coal tar Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas Coal gas is a flammable gaseous fuel Fuel gas is any one of a number of fuels that under ordinary conditions are gaseous. Many fuel gases are c ...
. Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method. Gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. In 1855, Hofmann used the word "
aromatic In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in ...
" to designate this family relationship, after a characteristic property of many of its members. In 1997, benzene was detected in deep space.


Ring formula

The empirical formula for benzene was long known, but its highly
polyunsaturated In nutrition Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided ...
structure, with just one
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
atom for each
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
atom, was challenging to determine. Archibald Scott Couper in 1858 and
Johann Josef Loschmidt Johann Josef Loschmidt (15 March 1821 – 8 July 1895), who referred to himself mostly as Josef Loschmidt (omitting his first name), was a notable Austria Austria (, ; german: Österreich ), officially the Republic of Austria (german: R ...

Johann Josef Loschmidt
in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but too little evidence was then available to help chemists decide on any particular structure. In 1865, the German chemist Friedrich
August Kekulé Friedrich August Kekulé, later Friedrich August Kekule von Stradonitz ( , ; 7 September 1829 – 13 July 1896), was a German organic chemist. From the 1850s until his death, Kekulé was one of the most prominent chemists in Europe, especially i ...
published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds. The next year he published a much longer paper in German on the same subject. Kekulé used evidence that had accumulated in the intervening years—namely, that there always appeared to be only one
isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulas — that is, same number of atoms of each element (chemistry), element — but distinct arrangements of atoms in space. Isomerism is existence or possibil ...

isomer
of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every disubstituted derivative—now understood to correspond to the ortho, meta, and para patterns of arene substitution—to argue in support of his proposed structure. Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio. The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating the twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory. He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail (this is a common symbol in many ancient cultures known as the
Ouroboros The ouroboros or uroboros () is an ancient symbol depicting a serpent (symbolism), serpent or European dragon, dragon self-cannibalism, eating its own tail. The ouroboros entered Western tradition via Egyptian mythology, ancient Egyptian iconogra ...

Ouroboros
or
Endless knot file:Endless knot detail, from- Burmese-Pali Manuscript. Wellcome L0026495 (cropped).jpg, Endless Knot in a Burmese Pali Manuscript The endless knot or eternal knot (Sanskrit: Shrivatsa, śrīvatsa; ; Tibetic languages, Tibetan དཔལ་ ...
). This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. This was 7 years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time. Curiously, a similar, humorous depiction of benzene had appeared in 1886 in a pamphlet entitled ''Berichte der Durstigen Chemischen Gesellschaft'' (Journal of the Thirsty Chemical Society), a parody of the ''Berichte der Deutschen Chemischen Gesellschaft'', only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote. Some historians have suggested that the parody was a lampoon of the snake anecdote, possibly already well known through oral transmission even if it had not yet appeared in print. Kekulé's 1890 speech in which this anecdote appeared has been translated into English. If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862. The cyclic nature of benzene was finally confirmed by the
Kathleen Lonsdale Dame Kathleen Lonsdale (née Yardley; 28 January 1903 – 1 April 1971) was an Irish pacifist Pacifism is opposition to war, militarism (including conscription Conscription, sometimes called the draft in the United States, is the man ...
in 1929.


Nomenclature

The German chemist Wilhelm Körner suggested the prefixes ortho-, meta-, para- to distinguish di-substituted benzene derivatives in 1867; however, he did not use the prefixes to distinguish the relative positions of the substituents on a benzene ring. It was the German chemist Karl Gräbe who, in 1869, first used the prefixes ortho-, meta-, para- to denote specific relative locations of the substituents on a di-substituted aromatic ring (viz, naphthalene). In 1870, the German chemist
Viktor Meyer Viktor Meyer (8 September 18488 August 1897) was a German chemist and significant contributor to both organic and inorganic chemistry. He is best known for inventing an apparatus for determining vapour densities, the Viktor Meyer apparatus, and ...

Viktor Meyer
first applied Gräbe's nomenclature to benzene.


Early applications

In the 19th and early 20th centuries, benzene was used as an after-shave lotion because of its pleasant smell. Prior to the 1920s, benzene was frequently used as an industrial solvent, especially for
degreasing Degreasing, often called defatting or fat trimming, is the removal of fatty acids from an object. In culinary Culinary arts, in which '' culinary'' means "related to cooking Cooking or cookery is the art, science, and craft of using heat to ...
metal. As its toxicity became obvious, benzene was supplanted by other solvents, especially
toluene Toluene (), also known as toluol (), is an aromatic hydrocarbon. It is a colorless, Water (molecule), water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group ( ...

toluene
(methylbenzene), which has similar physical properties but is not as carcinogenic. In 1903,
Ludwig Roselius Ludwig Roselius (2 June 1874 – 15 May 1943) was a German coffee merchant and founder of the company Kaffee HAG. He was born in Bremen and is credited with the development of commercial decaffeination of coffee. As a patron Patronage is ...
popularized the use of benzene to decaffeinate
coffee Coffee is a drink prepared from roasted s, the seeds of from certain s in the ' genus. From the coffee fruit, the seeds are separated to produce a stable, raw product: unroasted ''green coffee''. The seeds are then , a process which transfo ...

coffee
. This discovery led to the production of
Sanka 300px, 1932 advertisement for Sanka (USA) Sanka is a brand of instant decaffeinated coffee Coffee is a brewed drink prepared from roasted coffee beans, the seeds of berries from certain '' Coffea'' species. When coffee berries turn fr ...

Sanka
. This process was later discontinued. Benzene was historically used as a significant component in many consumer products such as Liquid Wrench, several
paint stripper Paint stripper, or paint remover, is a chemical product designed to remove paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is ...
s,
rubber cement Rubber cement (cow gum in British English) is an adhesive made from elastic polymers (typically natural rubber, latex) mixed in a solvent such as acetone, hexane, heptane or toluene to keep it fluid enough to be used. This makes it part of the clas ...
s, spot removers, and other products. Manufacture of some of these benzene-containing formulations ceased in about 1950, although Liquid Wrench continued to contain significant amounts of benzene until the late 1970s.


Occurrence

Trace amounts of benzene are found in petroleum and coal. It is a byproduct of the incomplete combustion of many materials. For commercial use, until
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a global war A world war is "a war War is an intense armed conflict between states State may refer to: Arts, entertainment, and media Literatur ...
, most benzene was obtained as a by-product of coke production (or "coke-oven light oil") for the
steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appe ...

steel
industry. However, in the 1950s, increased demand for benzene, especially from the growing
polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidiaries: ** Poly Property, a Hong Kong inc ...

polymer
s industry, necessitated the production of benzene from petroleum. Today, most benzene comes from the
petrochemical industry The petrochemical industry is concerned with the production and trade of petrochemicals Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum Petroleum (), also known as crude oil and oil, is a ...
, with only a small fraction being produced from coal. Benzene molecules have been detected on
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury (planet), Mercury. In English, Mars carries the name of the Mars (mythology), Roman god of war and is often referred to ...

Mars
.


Structure

X-ray diffraction X-ray crystallography (XRC) is the experimental science determining the atomic and molecular structure of a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a ...
shows that all six carbon-carbon bonds in benzene are of the same length, at 140
picometre The picometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: pm) or picometer ( American spelling) is a unit of length in the metric system, equal to , or one trillionth of a metre The m ...
s (pm). The C–C
bond length Bond or bonds may refer to: Common meanings * Bond (finance) In finance Finance is the study of financial institutions, financial markets and how they operate within the financial system. It is concerned with the creation and management of ...
s are greater than a double bond (135 pm) but shorter than a single bond (147 pm). This intermediate distance is caused by electron
delocalization 200px, Benzene, with the delocalization of the electrons indicated by the circle.">electron.html" ;"title="Benzene, with the delocalization of the electron">Benzene, with the delocalization of the electrons indicated by the circle. In chemistry, d ...
: the electrons for C=C bonding are distributed equally between each of the six carbon atoms. Benzene has 6 hydrogen atoms, fewer than the corresponding parent
alkane In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, pr ...
,
hexane Hexane () is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

hexane
, which has 14. Benzene and cyclohexane have a similar structure, only the ring of delocalized electrons and the loss of one hydrogen per carbon distinguishes it from cyclohexane. The molecule is planar. The molecular orbital description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the valence bond description involves a superposition of
resonance structures In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they und ...
. It is likely that this stability contributes to the peculiar molecular and chemical properties known as
aromaticity In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
. To accurately reflect the nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms. Derivatives of benzene occur sufficiently often as a component of organic molecules that the
Unicode Unicode, formally the Unicode Standard, is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expressed in most of the world's wri ...

Unicode
Consortium has allocated a symbol in the
Miscellaneous Technical Miscellaneous Technical is a Unicode blockA Unicode block is one of several contiguous ranges of numeric character codes ( code points) of the Unicode Unicode is an information technology Technical standard, standard for the consistent charac ...
block with the code U+232C (⌬) to represent it with three double bonds, and U+23E3 (⏣) for a delocalized version.


Benzene derivatives

Many important chemical compounds are derived from benzene by replacing one or more of its hydrogen atoms with another
functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions re ...
. Examples of simple benzene derivatives are
phenol Phenol (also called carbolic acid) is an aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), plane (geometry), p ...

phenol
,
toluene Toluene (), also known as toluol (), is an aromatic hydrocarbon. It is a colorless, Water (molecule), water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group ( ...

toluene
, and
aniline Aniline is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and sy ...

aniline
, abbreviated PhOH, PhMe, and PhNH2, respectively. Linking benzene rings gives
biphenyl Biphenyl (also known as diphenyl, phenylbenzene, 1,1′-biphenyl, lemonene or BP) is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hy ...

biphenyl
, C6H5–C6H5. Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as
naphthalene Naphthalene is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavio ...

naphthalene
,
anthracene Anthracene is a solid polycyclic aromatic hydrocarbon (PAH) of formula C14H10, consisting of three fused benzene Benzene is an organic chemical compound A chemical compound is a chemical substance composed of many identical molecules (or ...

anthracene
,
phenanthrene Phenanthrene is a likely carcinogenic compound that poses a large toxicity risk to exposed living organisms. However, according to IARC, it is not identified as probable, possible or confirmed human carcinogen. It is a polycyclic aromatic hydroca ...

phenanthrene
, and
pyrene Pyrene is a polycyclic aromatic hydrocarbon (PAH) consisting of four fused benzene rings, resulting in a flat aromatic system. The chemical formula is . This yellow solid is the smallest peri-fused PAH (one where the rings are fused through m ...

pyrene
. The limit of the fusion process is the hydrogen-free allotrope of carbon,
graphite Graphite (), archaically referred to as plumbago, is a Crystallinity, crystalline form of the element carbon with its atoms arranged in a Hexagonal crystal system, hexagonal structure. It occurs naturally in this form and is the most stable for ...

graphite
. In heterocycles, carbon atoms in the benzene ring are replaced with other elements. The most important variations contain
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
. Replacing one CH with N gives the compound
pyridine Pyridine is a basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming language In computer science Computer science deals with the theoretical foundations of informati ...

pyridine
, C5H5N. Although benzene and pyridine are ''structurally'' related, benzene cannot be converted into pyridine. Replacement of a second CH bond with N gives, depending on the location of the second N,
pyridazine Pyridazine is a heterocyclic organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Cat ...
,
pyrimidine Pyrimidine is an aromatic In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts ...

pyrimidine
, or
pyrazine Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2. It is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. Pyrazine and a variety of alkylpyrazine, a ...
.


Production

Four chemical processes contribute to industrial benzene production:
catalytic reforming Catalytic reforming is a chemical process used to convert petroleum refinery An oil refinery or petroleum refinery is an List of industrial processes, industrial process Factory, plant where crude oil is transformed and refined into useful produc ...
,
toluene Toluene (), also known as toluol (), is an aromatic hydrocarbon. It is a colorless, Water (molecule), water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group ( ...

toluene
hydrodealkylation, toluene disproportionation, and
steam cracking Steam cracking is a petrochemical process in which saturated hydrocarbons are broken down into smaller, often unsaturated, hydrocarbons. It is the principal industrial method for producing the lighter alkene , the simplest alkene. In chemistr ...

steam cracking
. According to the
ATSDR The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal public health List of United States federal agencies, agency within the United States Department of Health and Human Services. The agency focuses on minimizing human health ...
Toxicological Profile for benzene, between 1978 and 1981, catalytic reformates accounted for approximately 44–50% of the total U.S benzene production.


Catalytic reforming

In catalytic reforming, a mixture of
hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structures, it is difficult to generalize furth ...
s with boiling points between 60–200 °C is blended with
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
gas and then exposed to a
bifunctionalIn organic chemistry, when a single organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability t ...
platinum chloride or
rhenium Rhenium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

rhenium
chloride
catalyst Catalysis () is the process of increasing the rate of a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In cla ...

catalyst
at 500–525 °C and pressures ranging from 8–50 atm. Under these conditions,
aliphatic In organic chemistry, hydrocarbon In organic chemistry, a hydrocarbon is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen che ...
hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons. The aromatic products of the reaction are then separated from the reaction mixture (or reformate) by extraction with any one of a number of
solvent A solvent (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...

solvent
s, including
diethylene glycol Diethylene glycol (DEG) is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, m ...

diethylene glycol
or
sulfolane Sulfolane (also ''tetramethylene sulfone'', systematic name: 1λ6-thiolane-1,1-dione) is an organosulfur compound Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest ...
, and benzene is then separated from the other aromatics by distillation. The extraction step of aromatics from the reformate is designed to produce aromatics with lowest non-aromatic components. Recovery of the aromatics, commonly referred to as BTX (benzene, toluene and xylene isomers), involves such extraction and distillation steps. In similar fashion to this catalytic reforming, UOP and commercialized a method from LPG (mainly propane and butane) to aromatics.


Toluene hydrodealkylation

Toluene hydrodealkylation converts
toluene Toluene (), also known as toluol (), is an aromatic hydrocarbon. It is a colorless, Water (molecule), water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group ( ...

toluene
to benzene. In this hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a chromium, molybdenum, or platinum oxide catalyst at 500–650 °C and 20–60 atm pressure. Sometimes, higher temperatures are used instead of a catalyst (at the similar reaction condition). Under these conditions, toluene undergoes dealkylation to benzene and methane: :C6H5CH3 + H2 → C6H6 + CH4 This irreversible reaction is accompanied by an equilibrium side reaction that produces
biphenyl Biphenyl (also known as diphenyl, phenylbenzene, 1,1′-biphenyl, lemonene or BP) is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hy ...

biphenyl
(aka diphenyl) at higher temperature: :2 + If the raw material stream contains much non-aromatic components (paraffins or naphthenes), those are likely decomposed to lower hydrocarbons such as methane, which increases the consumption of hydrogen. A typical reaction yield exceeds 95%. Sometimes, xylenes and heavier aromatics are used in place of toluene, with similar efficiency. This is often called "on-purpose" methodology to produce benzene, compared to conventional BTX (benzene-toluene-xylene) extraction processes.


Toluene disproportionation

Toluene disproportionation (TDP) is the conversion of toluene to benzene and xylene. Given that demand for ''para''-xylene (P-Xylene, ''p''-xylene) substantially exceeds demand for other xylene isomers, a refinement of the TDP process called Selective TDP (STDP) may be used. In this process, the xylene stream exiting the TDP unit is approximately 90% ''p''-xylene. In some systems, even the benzene-to-xylenes ratio is modified to favor xylenes.


Steam cracking

Steam cracking is the process for producing ethylene and other alkenes from Aliphatic compound, aliphatic hydrocarbons. Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid by-product called ''pyrolysis gasoline''. Pyrolysis gasoline can be blended with other hydrocarbons as a gasoline additive, or routed through an extraction process to recover BTX aromatics (benzene, toluene and xylenes).


Other methods

Although of no commercial significance, many other routes to benzene exist. Phenol and halobenzenes can be reduced with metals. Benzoic acid and its salts undergo decarboxylation to benzene. The reaction of the diazonium compound derived from
aniline Aniline is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and sy ...

aniline
with hypophosphorus acid gives benzene. Trimerization of acetylene gives benzene.


Uses

Benzene is used mainly as an intermediate to make other chemicals, above all
ethylbenzene Ethylbenzene is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, cat ...
,
cumene Cumene (isopropylbenzene) is an organic compound that is based on an aromatic hydrocarbon with an aliphatic substitution. It is a constituent of crude oil and refined fuels. It is a flammable colorless liquid that has a boiling point of 152&nbs ...

cumene
, cyclohexane, nitrobenzene, and alkylbenzene. More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene, which is used to make polymers and plastics like polystyrene and EPS. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce
phenol Phenol (also called carbolic acid) is an aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), plane (geometry), p ...

phenol
and acetone for resins and adhesives. Cyclohexane consumes around 10% of the world's benzene production; it is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. In 2013, the biggest consumer country of benzene was China, followed by the USA. Benzene production is currently expanding in the Middle East and in Africa, whereas production capacities in Western Europe and North America are stagnating. Toluene is now often used as a substitute for benzene, for instance as a fuel additive. The solvent-properties of the two are similar, but toluene is less toxic and has a wider liquid range. Toluene is also processed into benzene. File:Benzene_uses.png, center, Major commodity chemicals and polymers derived from benzene. Clicking on the image loads the appropriate article, 600px, thumb rect 39 660 435 807 #Uses, Benzene rect 665 60 1062 207 Ethylbenzene rect 665 426 1062 579 Cumene rect 665 795 1062 942 Cyclohexane rect 665 1161 1062 1317 Aniline rect 665 1533 1062 1686 Chlorobenzene rect 1215 345 1614 495 Acetone rect 1215 636 1614 783 Phenol rect 1764 57 2163 210 Styrene rect 1764 432 2163 585 Bisphenol A rect 1764 1083 2163 1233 Adipic acid rect 1764 1332 2163 1482 Caprolactam rect 2313 57 2712 207 Polystyrene rect 2313 315 2712 462 Polycarbonate rect 2313 570 2712 717 Epoxy resin rect 2313 822 2712 975 Phenolic resin rect 2313 1083 2712 1233 Nylon 6-6 rect 2313 1335 2712 1485 Nylon 6 desc bottom-left


Component of gasoline

As a gasoline (petrol) additive, benzene increases the octane rating and reduces Engine knocking, knocking. As a consequence, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced it as the most widely used antiknock additive. With the global phaseout of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. In the United States, concern over its negative health effects and the possibility of benzene's entering the groundwater have led to stringent regulation of gasoline's benzene content, with limits typically around 1%. European petrol specifications now contain the same 1% limit on benzene content. The United States Environmental Protection Agency introduced new regulations in 2011 that lowered the benzene content in gasoline to 0.62%. In many European languages, the word for petroleum or gasoline is an exact cognate of "benzene".


Reactions

The most common reactions of benzene involve substitution of a proton by other groups. Electrophilic aromatic substitution is a general method of derivatizing benzene. Benzene is sufficiently nucleophile, nucleophilic that it undergoes substitution by acylium ions and alkyl carbocations to give substituted derivatives. : The most widely practiced example of this reaction is the ethylation of benzene. :: Approximately 24,700,000 tons were produced in 1999. Highly instructive but of far less industrial significance is the Friedel-Crafts alkylation of benzene (and many other aromatic rings) using an alkyl halide in the presence of a strong Lewis acid catalyst. Similarly, the Friedel-Crafts acylation is a related example of electrophilic aromatic substitution. The reaction involves the acylation of benzene (or many other aromatic rings) with an acyl chloride using a strong Lewis acid
catalyst Catalysis () is the process of increasing the rate of a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In cla ...

catalyst
such as aluminium chloride or Iron(III) chloride.


Sulfonation, chlorination, nitration

Using electrophilic aromatic substitution, many functional groups are introduced onto the benzene framework. Aromatic sulfonation, Sulfonation of benzene involves the use of oleum, a mixture of sulfuric acid with sulfur trioxide. Sulfonated benzene derivatives are useful detergents. In nitration, benzene reacts with nitronium ions (NO2+), which is a strong electrophile produced by combining sulfuric and nitric acids. Nitrobenzene is the precursor to
aniline Aniline is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and sy ...

aniline
. Chlorination is achieved with chlorine to give chlorobenzene in the presence of a Lewis acid catalyst such as aluminium tri-chloride.


Hydrogenation

Via hydrogenation, benzene and its derivatives convert to cyclohexane and derivatives. This reaction is achieved by the use of high pressures of
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
in the presence of heterogeneous catalysts, such as finely divided nickel. Whereas alkenes can be hydrogenated near room temperatures, benzene and related compounds are more reluctant substrates, requiring temperatures >100 °C. This reaction is practiced on a large scale industrially. In the absence of the catalyst, benzene is impervious to hydrogen. Hydrogenation cannot be stopped to give cyclohexene or cyclohexadienes as these are superior substrates. Birch reduction, a non catalytic process, however selectively hydrogenates benzene to the diene.


Metal complexes

Benzene is an excellent ligand in the complex (chemistry), organometallic chemistry of low-valent metals. Important examples include the sandwich and half-sandwich complexes, respectively, Bis(benzene)chromium, Cr(C6H6)2 and (Benzene)ruthenium dichloride dimer, [RuCl2(C6H6)]2.


Health effects

Benzene is classified as a carcinogen, which increases the risk of cancer and other illnesses, and is also a notorious cause of bone marrow failure. Substantial quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia, bone marrow abnormalities and cardiovascular disease. The specific hematologic malignancies that benzene is associated with include: acute myeloid leukemia (AML), aplastic anemia, myelodysplastic syndrome (MDS), acute lymphoblastic leukemia (ALL), and chronic myeloid leukemia (CML). The American Petroleum Institute (API) stated in 1948 that "it is generally considered that the only absolutely safe concentration for benzene is zero". There is no safe exposure level; even tiny amounts can cause harm. The US Department of Health and Human Services (DHHS) classifies benzene as a human carcinogen. Long-term exposure to excessive levels of benzene in the air causes leukemia, a potentially fatal cancer of the blood-forming organs. In particular, acute myeloid leukemia or acute nonlymphocytic leukemia (AML & ANLL) is not disputed to be caused by benzene. IARC rated benzene as "known to be carcinogenic to humans" (Group 1). As benzene is ubiquitous in gasoline and hydrocarbon fuels that are in use everywhere, human exposure to benzene is a global health problem. Benzene targets the liver, kidney, lung, heart and brain and can cause DNA strand breaks, chromosomal damage, etc. Benzene causes cancer in animals including humans. Benzene has been shown to cause cancer in both sexes of multiple species of laboratory animals exposed via various routes.


Exposure to benzene

According to the Agency for Toxic Substances and Disease Registry (ATSDR) (2007), benzene is both a man-made and naturally occurring chemical from processes that include: volcanic eruptions, wild fires, synthesis of chemicals such as
phenol Phenol (also called carbolic acid) is an aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), plane (geometry), p ...

phenol
, production of synthetic fibers, and fabrication of rubbers, lubricants, pesticides, medications, and dyes. The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions; however, ingestion and dermal absorption of benzene can also occur through contact with contaminated water. Benzene is hepatically metabolized and excreted in the urine. Measurement of air and water levels of benzene is accomplished through collection via activated charcoal tubes, which are then analyzed with a gas chromatograph. The measurement of benzene in humans can be accomplished via Urine test, urine, Blood test, blood, and breath tests; however, all of these have their limitations because benzene is rapidly metabolized in the human body. Exposure to benzene may lead progressively to aplastic anemia, leukaemia, and multiple myeloma. Occupational Safety and Health Administration, OSHA regulates levels of benzene in the workplace. The maximum allowable amount of benzene in workroom air during an 8-hour workday, 40-hour workweek is 1 ppm. As benzene can cause cancer, National Institute for Occupational Safety and Health, NIOSH recommends that all workers wear special Self-contained breathing apparatus, breathing equipment when they are likely to be exposed to benzene at levels exceeding the recommended (8-hour) exposure limit of 0.1 ppm.


Benzene exposure limits

The United States Environmental Protection Agency has set a maximum contaminant level (MCL) for benzene in drinking water at 0.005 mg/L (5 ppb), as promulgated via the U.S. National Primary Drinking Water Regulations. This regulation is based on preventing benzene leukemogenesis. The maximum contaminant level goal (MCLG), a nonenforceable health goal that would allow an adequate margin of safety for the prevention of adverse effects, is zero benzene concentration in drinking water. The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported. The U.S. Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 1 part of benzene per million parts of air (1 ppm) in the workplace during an 8-hour workday, 40-hour workweek. The short term exposure limit for airborne benzene is 5 ppm for 15 minutes. These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. The risk from exposure to 1 ppm for a working lifetime has been estimated as 5 excess leukemia deaths per 1,000 employees exposed. (This estimate assumes no threshold for benzene's carcinogenic effects.) OSHA has also established an action level of 0.5 ppm to encourage even lower exposures in the workplace. The U.S. National Institute for Occupational Safety and Health (NIOSH) revised the Immediately Dangerous to Life and Health (IDLH) concentration for benzene to 500 ppm. The current NIOSH definition for an IDLH condition, as given in the NIOSH Respirator Selection Logic, is one that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment [NIOSH 2004]. The purpose of establishing an IDLH value is (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) is considered a maximum level above which only a highly reliable Self-contained breathing apparatus, breathing apparatus providing maximum worker protection is permitted [NIOSH 2004]. In September 1995, NIOSH issued a new policy for developing recommended exposure limits (RELs) for substances, including carcinogens. As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the REL (10-hour) of 0.1 ppm. The NIOSH short-term exposure limit (STEL – 15 min) is 1 ppm. American Conference of Governmental Industrial Hygienists (ACGIH) adopted Threshold Limit Values (TLVs) for benzene at 0.5 ppm TWA and 2.5 ppm STEL.


Toxicology


Biomarkers of exposure

Several tests can determine exposure to benzene. Benzene itself can be measured in breath, blood or urine, but such testing is usually limited to the first 24 hours post-exposure due to the relatively rapid removal of the chemical by exhalation or biotransformation. Most people in developed countries have measureable baseline levels of benzene and other aromatic petroleum hydrocarbons in their blood. In the body, benzene is enzymatically converted to a series of oxidation products including muconic acid, phenylmercapturic acid,
phenol Phenol (also called carbolic acid) is an aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), plane (geometry), p ...

phenol
, catechol, hydroquinone and Hydroxyquinol, 1,2,4-trihydroxybenzene. Most of these metabolites have some value as biomarkers of human exposure, since they accumulate in the urine in proportion to the extent and duration of exposure, and they may still be present for some days after exposure has ceased. The current ACGIH biological exposure limits for occupational exposure are 500 μg/g creatinine for muconic acid and 25 μg/g creatinine for phenylmercapturic acid in an end-of-shift urine specimen.


Biotransformations

Even if it is not a common substrate for metabolism, benzene can be oxidized by both bacteria and eukaryotes. In bacteria, dioxygenase enzyme can add an oxygen to the ring, and the unstable product is immediately reduced (by NADH) to a cyclic diol with two double bonds, breaking the aromaticity. Next, the diol is newly reduced by NADH to catechol. The catechol is then metabolized to acetyl CoA and succinyl CoA, used by organisms mainly in the Citric Acid Cycle for energy production. The pathway for the metabolism of benzene is complex and begins in the liver. Several enzymes are involved. These include cytochrome P450 2E1 (CYP2E1), quinine oxidoreductase (NQ01 or DT-diaphorase or NAD(P)H dehydrogenase (quinone 1)), GSH, and myeloperoxidase (MPO). CYP2E1 is involved at multiple steps: converting benzene to oxepin (benzene oxide),
phenol Phenol (also called carbolic acid) is an aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), plane (geometry), p ...

phenol
to hydroquinone, and hydroquinone to both benzenetriol and catechol. Hydroquinone, benzenetriol and catechol are converted to polyphenols. In the bone marrow, MPO converts these polyphenols to benzoquinones. These intermediates and metabolites induce genotoxicity by multiple mechanisms including inhibition of topoisomerase II (which maintains chromosome structure), disruption of microtubules (which maintains cellular structure and organization), generation of oxygen free radicals (unstable species) that may lead to point mutations, increasing oxidative stress, inducing DNA strand breaks, and altering DNA methylation (which can affect gene expression). NQ01 and GSH shift metabolism away from toxicity. NQ01 metabolizes benzoquinone toward polyphenols (counteracting the effect of MPO). GSH is involved with the formation of phenylmercapturic acid. Genetic polymorphisms in these enzymes may induce loss of function or gain of function. For example, mutations in CYP2E1 increase activity and result in increased generation of toxic metabolites. NQ01 mutations result in loss of function and may result in decreased detoxification. Myeloperoxidase mutations result in loss of function and may result in decreased generation of toxic metabolites. GSH mutations or deletions result in loss of function and result in decreased detoxification. These genes may be targets for genetic screening for susceptibility to benzene toxicity.


Molecular toxicology

The paradigm of toxicological assessment of benzene is shifting towards the domain of molecular toxicology as it allows understanding of fundamental biological mechanisms in a better way. Glutathione seems to play an important role by protecting against benzene-induced DNA breaks and it is being identified as a new biomarker for exposure and effect. Benzene causes chromosomal aberrations in the peripheral blood leukocytes and bone marrow explaining the higher incidence of leukemia and multiple myeloma caused by chronic exposure. These aberrations can be monitored using fluorescent in situ hybridization (FISH) with DNA probes to assess the effects of benzene along with the hematological tests as markers of hematotoxicity. Benzene metabolism involves enzymes coded for by polymorphic genes. Studies have shown that genotype at these loci may influence susceptibility to the toxic effects of benzene exposure. Individuals carrying variant of NAD(P)H:quinone oxidoreductase 1 (NQO1), microsomal epoxide hydrolase (EPHX) and deletion of the glutathione S-transferase T1 (GSTT1) showed a greater frequency of DNA single-stranded breaks.


Biological oxidation and carcinogenic activity

One way of understanding the carcinogenic effects of benzene is by examining the products of biological oxidation. Pure benzene, for example, oxidizes in the body to produce an epoxide, benzene oxide, which is not excreted readily and can interact with DNA to produce harmful mutations.


Routes of exposure


Inhalation

Outdoor air may contain low levels of benzene from automobile service stations, wood smoke, tobacco smoke, the transfer of gasoline, exhaust from motor vehicles, and industrial emissions. About 50% of the entire nationwide (United States) exposure to benzene results from smoking tobacco or from exposure to tobacco smoke. After smoking 32 cigarettes per day, the smoker would take in about 1.8 milligrams (mg) of benzene. This amount is about 10 times the average daily intake of benzene by nonsmokers. Inhaled benzene is primarily expelled unchanged through exhalation. In a human study 16.4 to 41.6% of retained benzene was eliminated through the lungs within five to seven hours after a two- to three-hour exposure to 47 to 110 ppm and only 0.07 to 0.2% of the remaining benzene was excreted unchanged in the urine. After exposure to 63 to 405 mg/m3 of benzene for 1 to 5 hours, 51 to 87% was excreted in the urine as phenol over a period of 23 to 50 hours. In another human study, 30% of absorbed dermally applied benzene, which is primarily metabolized in the liver, was excreted as phenol in the urine.


Exposure from soft drinks

Under specific conditions and in the presence of other chemicals
benzoic acid Benzoic acid is a white (or colorless) solid with the formula C6H5CO2H. It is the simplest aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic ( ...

benzoic acid
(a preservative) and ascorbic acid (Vitamin C) may interact to produce benzene. In March 2006, the official Food Standards Agency in United Kingdom, Britain conducted a survey of 150 brands of soft drinks. It found that four contained benzene levels above World Health Organization limits. The affected batches were removed from sale. Similar problems were reported by the FDA in the United States.


Contamination of water supply

In 2005, the water supply to the city of Harbin in China with a population of almost nine million people, was cut off because of a major benzene exposure. Benzene leaked into the Songhua River, which supplies drinking water to the city, after Jilin chemical plant explosions 2005, an explosion at a China National Petroleum Corporation (CNPC) factory in the city of Jilin on 13 November, 2005. When plastic water pipes are subject to high heat, the water may be contaminated with benzene.


Murder

The Nazis used benzene administered via Injection (medicine), injection as one of their many methods for murder, killing.


See also

* 6-membered aromatic rings with one carbon replaced by another group: borabenzene, benzene, silabenzene, germabenzene, stannabenzene,
pyridine Pyridine is a basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming language In computer science Computer science deals with the theoretical foundations of informati ...

pyridine
, phosphorine, arsabenzene, pyrylium salt * Industrial Union Department v. American Petroleum Institute * BTEX


Notes


References


External links


Benzene
at ''The Periodic Table of Videos'' (University of Nottingham)
International Chemical Safety Card 0015




*
Dept. of Health and Human Services: TR-289: Toxicology and Carcinogenesis Studies of Benzene

Video Podcast
of Sir John Cadogan giving a lecture on Benzene since Faraday, in 1991
Substance profile
*
NLM Hazardous Substances Databank – Benzene
{{Authority control Benzene, Annulenes Aromatic hydrocarbons Simple aromatic rings IARC Group 1 carcinogens Soil contamination Hydrocarbon solvents Hazardous air pollutants Immunotoxins Mutagens Teratogens Occupational safety and health Carcinogens Commodity chemicals Petrochemicals GABAA receptor positive allosteric modulators Aromatic solvents Six-membered rings